Pharmacomorphological study of denervation induced by 6-hydroxydopamine in Porichthys photophores

The effects of 6-hydroxydopamine (6-OHDA) on the bioluminescent response of Porichthys photophores were investigated as part of a pharmacological study of the neural control of luminescence in this fish. Subcutaneous injections of 6-OHDA induce a luminescent response similar to that of norepinephrine (NE), suggesting a sympathomimetic action. The luminescent response to electrical stimulation is almost completely and irreversibly abolished within 24 hours following low-dose treatment of the photophores with 6-OHDA, while the sensitivity of these organs to exogenous NE is increased significantly over the few days post-treatment. During this period the photophores continuously emitted a steady low-level glow. Electronmicroscopic studies of such photophores revealed progressive destruction of the nerve endings. Photophore luminescent sensitivity to NE subsequently became sub-normal, and at this stage electron microscopy revealed an increasingly larger number of damaged photocytes, supportive cells and, in one case, lens cells. From these results it is suggested that 6-OHDA initially impairs neuro-photocyte transmission by destroying catecholaminergic nerve endings. In turn, the transmitter reuptake mechanism is also impaired, thus accounting for development of supersensitive responses to exogenous NE. Subnormal luminescent responses to NE appear as a result of loss of photocyte competence due to structural deterioration. The latter are interpreted as the consequence of removal of trophic factors supplied by the photophore adrenergic innervation.Suppression of luminescent response to both electrical stimulation and exogenous NE in photophores treated with higher doses of 6-OHDA, may be due to a direct effect of this drug on the receptor sites of the photocytes.     

“South American” Marsupials from the Late Cretaceous of North America and the Origin of Marsupial Cohorts

Newly described marsupial specimens of Judithian (late Campanian) and Lancian (Maastrichtian) age in the western interior of North America (Wyoming to Alberta) have dental morphologies consistent with those expected in comparably aged sediments in South America (yet to be found). Three new Lancian species are referable to the didelphimorphian Herpetotheriidae, which suggests that the ameridelphian radiation was well under way by this time. The presence of a polydolopimorphian from Lancian deposits with a relatively plesiomorphic dental morphology and an additional polydolopimorphian taxon from Judithian deposits with a more derived molar form indicate that this lineage of typically South American marsupials was diversifying in the Late Cretaceous of North America. This study indicates that typical South American lineages (e.g. didelphimorphians and polydolopimorphians) are not the result of North American peradectian progenitors dispersing into South America at the end of the Cretaceous (Lancian), or at the beginning of the Paleocene (Puercan), and giving rise to the ameridelphian marsupials. Instead, these lineages, and predictably others as well, had their origins in North America (probably in more southerly latitudes) and then dispersed into South America by the end of the Cretaceous. Geophysical evidence concerning the connections between North and South America in the Late Cretaceous is summarized as to the potential for overland mammalian dispersal between these places at those times. Paleoclimatic reconstructions are considered, as is the dispersal history of hadrosaurine dinosaurs and boid snakes, as to their contribution to an appraisal of mammalian dispersals in the Late Cretaceous. In addition, we present a revision of the South American component of the Marsupialia. One major outcome of this process is that the Polydolopimorphia is placed as Supercohort Marsupialia incertae sedis because no characteristics currently known from this clade securely place it within one of the three named marsupial cohorts. This article contains corrections to the text and a new Figure 11 not incorporated in the originally published version in Vol. 11, Nos. 3/4. For purposes of future citation, the present version (Vol. 12 and Nos. 3/4) should be used.     

Control of flashing in fireflies

Summary The restrained male of the fireflyPteroptyx cribellata of Papua New Guinea responds to exogenous light signals with a latency of about one second, which equals the period of the natural spontaneous rhythm of flashing and includes about 800 ms of central nervous delay. The response is cycle-by-cycle and all-or-none and the duration of the response time is independent of the phasing of the driver in relation to the free run rhythm (Figs. 1, 2). The firefly can be entrained to rhythms over a period range of 800 ms to 1,600 ms, during which it leads or lags the concurrent signal by an amount equal to the difference between the driving period and the animal's period (Figs. 3, 4). The phase-response line is nearly straight and is inclined 45 ° (Figs. 2, 5). Normally an exogenous signal dictates interflash timing but occasionally may fail to entrain the firefly (Figs. 7B, E) or may fail to evoke a flash (Figs. 7F, G). Persistence of endogenous control of timing period duration even during driving is occasionally seen as spontaneous drift in response time (Fig. 9). It is proposed that during entrainment each exogenous signal resets the pacemaker immediately to the start of its endogenous cycle, from which point it then begins a new series of free run periods. Thus each flash is timed in relation to the signal of the preceding cycle (Fig. 3). We devised a model of the endogenous timing cycle which fits the empirical data and achieves entrainment by a single mechanism involving phase advance or delay rather than change in actual rate of endogenous timing (Fig. 12). The proposed mechanism by which single males entrain to light signals seems compatible also with the mass synchronous flashing which is the characteristic behavior of field congregations.We are much indebted to Drs. D. Alkon, T.H. Bullock, A. Carlson, F. Dodge, J. Enright, H. Gainer, R. Josephson, H.M. Pinsker, C.L. Prosser, A. Winfree and the late K. Roeder for various information, suggestions and editorial assistance. We thank especially Dr. Laurens Mets for valuable insights. The research was made possible by grants GB8158 and GB8400 from the National Science Foundation to the Scripps Institution of Oceanography in support of the 1969 Alpha Helix Expedition to New Guinea. Supplementary support was received by J.B. from the American Philosophical Society (Penrose Fund grant 5017) and the National Geographic Society; by J.F.C. from ONR Contract N0014-69-A-022-8006 and from the University of California Faculty Research Fund; by F.E.H. from a Faculty Grant, University of Texas. Mrs. Betty Morris cheerfully endured the typing of endless drafts.     

Molecular dynamics analysis of a ribonuclease C-peptide analogue

We have carried out a nanosecond molecular dynamics simulation of an analogue of the ribonuclease C-peptide in water. The overall conformation has an extended region for the first three amino acids connected to an α-helix for residues 4–13, and this basic structure is preserved throughout the simulation, with helical hydrogen bonds present 87% of the time, on average. The final helical hydrogen bond is spontaneously broken and re-formed several times, providing a detailed picture of such winding/unwinding events. The simulation was used to estimate the effects of internal motion on proton nuclear Overhauser effect spectroscopy (NOESY) intensities for several classes of important cross peaks. Within the helical regions, the effects of internal motion vary only a little from one residue to another for backbone–backbone cross peaks, and the relevant correlation functions reach plateau values within about 50 ps. The spectral simulations show, however, that it may be difficult to establish a close quantitative connection between NOESY cross-peak volumes and measures of helical content. © 1993 John Wiley & Sons, Inc.     

Physiological Links in Firefly Flash Code Evolution

New and reassessed neurophysiological observations on dialog fireflies permit (1) parsimonious inferences about the origin and fixation of light emission in the primeval firefly, (2) proof of widespread involvement of a stable species-specific minimal stimulus–response interval in timed flashing behaviors of both genders, (3) strengthening of the evidence for certain normally latent flash control intervals common to both male and female, (4) assignment of possible roles in the evolution of time-coded courting dialog to these data, and (5) evaluation of the evolutionary status of certain present-day species.